Gas discharge panels commonly known as plasma panels have a plurality of gas discharge cells and are constructed of a pair of crossing electrode arrays separated by an insulator from a gaseous medium. Coupling of an appropriate signal to a selected cell or location defined by a respective crossing electrode in each array causes the gas medium therebetween to discharge and to cause the formation of wall charges. The formed wall charges at the cell or location cooperate with alternating sustaining signals to respectively discharge the selected cell for as long as desired. Reference may be made to U.S. Pat. No. 3,559,190 "Gaseous Display and Memory Apparatus", D. L. Bitzer, H. G. Slottow and R. H. Willson, assigned to the University of Illinois Foundation which patent describes such a plasma panel and its operation.
Various techniques have been proposed and several are currently in use in order to uniquely address a particular gas discharge cell defined between a respective electrode in each of the matrix electrode arrays. The basic signal to be applied to a single electrode in each array of the display matrix in order to select one cell or location within that matrix normally is a pulse of approximately 50-150 volts in magnitude and approximately 2-5 microseconds in duration. In general, a positive going pulse is applied to one electrode in the first array and a negative going pulse to the second electrode in the other array associated with the selected cell. Thus, the selected cell discharges since the magnitude of the voltage across the cell is equal to twice the magnitude of the voltage applied to the selected single electrode of each array. However, the remainder of the cells respectively associated with the selected electrode in each array do not discharge since the voltage magnitude applied to the single selected electrode is not sufficient to do so. Therefore only one cell, the one defined at the junction of the addressed or selected electrodes in each array has an adequate signal applied to cause a discharge.
A major item in the total system cost of a plasma display device of this type is the cost of the generation of the addressing signals required. Several viable techniques have been previously demonstrated with the total component per line or electrode density reduced to two diodes and a single resistor for a total of three. Thus, a normal plasma display panel containing a 512 .times. 512 matrix array, requires a total of 3072 addressing components per panel. A normal communications system may contain anywhere from 10 to 1000 of such panels so that the number of components per system rapidly becomes significant. It therefore becomes extremely desirable to reduce the overall cost of a system incorporating plasma panels by reducing the number of components required per panel electrode to address a desired cell or location on the anel.
In the operation of plasma panels, it is desirable to provide a sustaining signal which can reliably repetitively discharge cells in the on state and yet which will not discharge cells which are in the off state. The range over which the sustaining signal amplitude can vary is bounded on the lower limit by the voltage which causes a cell in the on state to go into the off state, and on the upper limit by the voltage which causes a cell in the off state to go into the on state. The usable voltage range over which an applied sustaining signal can vary and satisfactory plasma panel operation obtained is defined as that range between the voltage at which the first on cell is caused to go off (i.e. first on-to-off cell) on the lower limit and the first off cell to go on (i.e. first off-to-on cell) at the upper limit.
Due to the fact that plasma panels provide an enormous number of cells (normally 512 .times. 512 cells) and the difficulty in manufacturing uniform plasma panels, measurements made on existing production plasma panels indicate that this usable voltage range with present sustaining signals can vary from 10-15% of the normal sustaining signal potential level of 120 volts. In other words, depending primarily on the characteristics of a particular plasma panel, the usable range of presently utilized sustaining signals can range from 12 volts for one panel to possibly 18 volts or more for another panel.
Suggestions or attempts have been made by others to increase the reliability of discharging an off cell to place it in the on state during addressing by inducing an overshoot in the leading edge of the addressing signal waveform which provides overcharging immediately before the actual cell discharge. However, attempts to apply an overshoot onto the leading edge of a sustaining signal waveform immediately before a sustaining discharge to improve the usable range have achieved only a very slight usable range increase. It becomes therefore extremely desirable to increase the usable range of sustaining signals so as to increase the reliability of the sustaining operation with any particular plasma panel and in order to provide an increased margin of acceptable panels for the plasma panel manufacturer.